Each of these rooms, or structures, plays a role in protecting your Shelter from Invasions. Some slow down enemies, some damage enemies, and some can be manned by Workers or Champions to attack invaders before they breach your Gate. There is a limit of four structures that can be built in front of your Gate. Initially, you will only be able to build one of each structure you have unlocked, but this increases so that by Shelter Level 8 you can build up to four of any of the structures (Barricade, Spikes, and Guard Tower). You are still limited to 4 total structures though.
¶ Balcony
Room Stat: DPS
The Balcony provides space for two characters to watch the front of your base and fire upon approaching attackers. The damage dealt by the guards in the Balcony is determined by their DPS, and their weapon does not need to be a ranged weapon. Some levels do not provide any upgrade apart from appearance, but at some levels the number of guards that can be stationed in the Balcony increases.
| Upgrade | Guards | |
| Shelter Level 4 | Unlocked | 2 |
| Shelter Level 14 | Level 2 | 2 |
| Shelter Level 24 | Level 3 | 3 |
¶ Barricade
Room Stat: No Workers
Barricades slow down approaching enemies, giving your guards in the Guard Towers and Balcony more time to shoot at them before they reach the Gate.
| Upgrade | Armor | Hit Points | |
| Shelter Level 4 | Unlocked | 50 | 50 |
| Shelter Level 14 | Level 2 | 100 | 50 |
| Shelter Level 24 | Level 3 | 300 | 40? |
¶ Gate
Room Stat: DPS
It's the door that holds the entrance to your Shelter. There is no way to defend it from outside once enemies are attacking the structure. Workers or Champions can be assigned to this room to fight off invaders.
| Upgrade | Armor | Hit Points | Guards | |
| Shelter Level 4 | Unlocked | 100 | 100 | 1 |
| Shelter Level 10 | Level 2 | 250 | 100 | 1 |
| Shelter Level 20 | Level 3 | 750 | 70 | 2 |
| Shelter Level 30 | Level 4 | ? | ? | ? |
¶ Guard Tower
Room Stat: DPS
The Guard Tower is much like the Balcony, but in front of your main building rather than attached to the building. Each tower can only hold one guard. Unlike the Balcony, they also provide some obstruction, slowing down enemies.
| Upgrade | Armor | Hit Points | Guards | |
| Shelter Level 8 | Unlocked | 30 | ? | 1 |
| Shelter Level 16 | Level 2 | 60 | 70 | 1 |
| Shelter Level 28 | Level 3 | 180 | 150 | 2 |
¶ Spikes
Room Stat: No Workers
Much like the Barricade, Spikes do not require any characters to man them. They do not slow enemies as significantly as a Barricade, but they slow enemies more than a Guard Tower and also deal damage to the enemies without requiring any guards manning them. They do appear to deal damage during invasions - even though their tool tip always lists them as having a DPS of 0.
| Upgrade | Armor | Hit Points | DPS | |
| Shelter Level 5 | Unlocked | 40 | ? | 0 |
| Shelter Level 14 | Level 2 | 80 | 40 | 0 |
| Shelter Level 26 | Level 3 | 240 | 100 | 0 |